JPH0679298B2 - Abnormality monitoring circuit for multi-drop serial bus transmission unit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission unit using a multidrop serial bus as a transmission path, and in particular, abnormality monitoring for preventing transmission system abnormality from spreading to the bus. Regarding the circuit.

B. SUMMARY OF THE INVENTION According to the present invention, in a transmission unit in which a transmission driver is connected to a multidrop serial bus by wire logic, an abnormality of a transmission data signal given to the transmission driver for a certain time or more continuously becomes an active level time monitoring circuit means. In addition, the gate circuit means is provided so as to fix the input of the transmission driver to the immovable level when the detection signal of this circuit means is generated. The system down state fixed to the active level can be avoided.

C. Prior art In a general transmission system using a multi-drop serial bus, each transmission driver of a large number of transmission units is wire-logic connected to the bus, and in each transmission system, the transmission data input of the transmission driver is fixed when not transmitting. It is fixed at the level, and 2 levels of active level and immovable level at the time of transmission
The configuration is such that the transmission data due to the value change is input to the transmission driver.

In this transmission system, when a certain transmission unit outputs an active level signal (in the case of an open collector type transmission driver, it outputs L level), the entire serial bus becomes active level. Therefore, if a failure occurs in the transmission system of a certain transmission unit and that transmission unit continues to output the active level signal, the bus will be fixed to the active level, so not only the faulty transmission unit The influence of the failure spreads to the entire system, and data cannot be transmitted between any units.
In other words, the system goes down.

In order to avoid this system down, the CPU that controls transmission and data processing in each transmission unit has been used in the past.
(Central processing unit) executes an abnormality diagnosis program, detects a fault such that the bus is fixed at an active level, and when the fault occurs in its own transmission unit, the transmission system of the unit is removed from the bus. It controls to disconnect. In this way, transmission using a bus is possible between sound units.

D, Problems to be Solved by the Invention As described above, the high-level abnormality diagnosis by the CPU can be relatively easily performed in the so-called intelligent terminal equipped with the CPU. However, in recent years, a multidrop serial bus type transmission system of this kind has been widely applied to various devices, and an example in which a simple sensor or an actuator driving circuit constitutes one transmission unit has come to be seen. Came. This kind of simple function unit does not have a sophisticated CPU, and therefore cannot diagnose the bus abnormality as seen in the intelligent terminal. Even if the transmission unit (functional unit) has a simple structure, some measures are necessary so that the failure of the own station does not render the entire bus system unusable.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is an extremely simple structure suitable for a functional unit having a simple structure that serves as one transmission unit, and a failure of its own station may occur in the entire bus system. It is an object of the present invention to provide an abnormality monitoring circuit for a transmission unit for a multidrop serial bus, which can prevent the transmission.

E, Means for Solving the Problems The abnormality monitoring circuit according to the present invention connects the transmission driver to the multidrop serial bus by wire logic,
At the time of non-transmission, the transmission data input of the transmission driver is fixed to the immobile level, and at the time of transmission, the active level and the immobility level are 2
In a transmission unit for inputting transmission data due to a change in value to the transmission driver, the transmission data signal is input, and time monitoring circuit means for issuing an output signal when this signal continuously reaches an active level for a certain period of time, Gate circuit means for receiving the output signal of the circuit means and fixing the input of the transmission driver at a fixed level.

F, Operation When the transmission data signal is fixed to the active level due to some abnormality, this abnormality is detected by the time monitoring circuit means after a fixed time, and the input of the transmission driver is immobile by the gate circuit means. Fixed to the level. As a result, the output of the transmission driver also becomes a fixed level and releases the bus,
Although data cannot be transmitted from the time station, data can be transmitted normally between other stations.

G, Embodiment FIG. 1 shows an embodiment of the abnormality monitoring circuit according to the present invention. In the figure, 10 is a multi-drop serial bus that serves as a data transmission line, and is connected to a power source through a pull-up resistor 12. Reference numeral 14 is a transmission driver composed of an open collector type inverter, the output of which is connected to the bus 10. The transmission drivers in many transmission units are similar open collector elements whose outputs are bus 10
Is connected to the wire logic.

The transmission data SD given from the data generation system (not shown)
It is input to the transmission driver 14 via the NOR gate 16. The transmission data SD is also input to a retriggerable monostable multivibrator (hereinafter referred to as monomulti) 18, and the output of the monomulti 18 becomes the other input of the NOR gate 16.

The mono-multi 18 corresponds to the time monitoring circuit means described above, and NOR
The gate 16 corresponds to the gate circuit means described above.

As shown in the waveform diagram of FIG. 2, the monomulti 18 is triggered at the falling point of the transmission data SD from the H level (immobility level) to the L level (active level), and the output changes from the H level to the L level. . The mono-multi 18 can be re-triggered, and the output returns from the L level to the H level if there is no next trigger signal even after a certain time TI has elapsed after being triggered.

When the output of Mono Multi 18 is at L level, NOR
The gate 16 is in a “gate open” state with respect to the transmission data SD, and the transmission data SD is output to the bus 10 via the NOR gate 16 and the transmission driver 14. This transmission state is shown in FIG.

As shown in FIG. 3, the transmission data is
When SD remains L level, the output of the monomulti 18 goes from L level to H level after a certain time TI. When the output goes to H level, it becomes NOR regardless of the transmission data SD.
The output of the gate 16 (that is, the input of the transmission driver 14) becomes the L level (which is the immovable level at this point), the output of the transmission driver 14 (the bus output) becomes the H level, and this transmission driver 14 is in the state of the bus 10. No longer be involved in.

H, Effect of the Invention As described in detail above, the abnormality monitoring circuit according to the present invention can be easily implemented by an extremely simple circuit including, for example, mono-multi, NOR gate, and extremely few circuit elements.
It is possible to reliably prevent a failure in the transmission system from spreading to the entire bus system. Therefore, the circuit is suitable for a simple function transmission unit without a CPU.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an abnormality monitoring circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram during normal transmission operation of the same circuit, and FIG. 3 is a waveform diagram when a failure similarly occurs. 10 …… bus, 14 …… send driver, 16 …… NOR gate, 1
8 …… A retriggerable monostable multivibrator.

Claims (1)

[Claims] 1. A transmission driver is connected to a multi-drop serial bus by wired logic, the transmission data input of the transmission driver is fixed to a down level when not transmitting, and transmission is performed by changing an active level and a down level binary value during transmission. A transmission unit for inputting data to the transmission driver receives the transmission data signal as an input, and outputs an output signal when the signal continuously goes to an active level for a certain period of time, and an output of the circuit unit. A gate circuit means for receiving a signal and fixing the input of the transmission driver to a lower level, the time monitoring circuit means being retriggerable monostable triggered at a change point of the active level of the transmission data signal. An abnormality monitoring circuit for a multi-drop serial bus transmission unit characterized by being a multi-vibrator.